Game apparatus and game program

ABSTRACT

In the game space, n light sources for irradiating an object with a light beam are set. A brightness calculating section  521  and a texture coordinate generating section  522  obtain, for each of predetermined units forming the object, a brightness vector having as components n illumination intensities respectively added by the n light sources. A texture color determining section  523  determines, for each of the predetermined units, a region including a tip of the brightness vector from among regions obtained via division by threshold values based on relationships in size between the n illumination intensities and their corresponding threshold values. A display color determining section  524  determines a display color for each of the predetermined units based on the region determined for each of the predetermined units, such that the object&#39;s display color distinctly varies.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a game apparatus and gameprogram, and more particularly to a game apparatus and game program fordisplaying an object using toon shading.

[0003] 2. Description of the Background Art

[0004] Conventionally, there are known image generating systems forgenerating an image viewed from a given viewpoint in a three-dimensionalvirtual space. Such systems are conventionally used in game apparatuses.Some of the systems generate a realistic image in order to improveartificial reality of a virtual space. Further, some of the systemsgenerate animated cartoon cell picture-like images in order to representthe virtual space in the manner of an animated cartoon. In such systems,an object in the virtual space is distinctly (i.e., clearly) shaded,thereby generating a cartoon-like image.

[0005] One conventional technology for generating the cartoon-like imageuses a so-called toon shading technique. FIG. 12 is a diagramillustrating an exemplary display of an image generated by theconventional technology using toon shading. A general process ofgenerating an image using toon shading is described below with referenceto FIG. 12. In this process, brightness information is initially addedto an object in a virtual space based on a prescribed condition. Forexample, the brightness information is added by irradiating the objectwith a light beam from a virtual light (light source) 91 provided at apoint in the virtual space. Then, the object is divided into a pluralityof portions in accordance with the brightness information. For example,consider a case of dividing the object into two grades (two areas). Theobject is divided into a bright area 92 and a dark area 93 in accordancewith brightness provided by the virtual light 91. Finally, color valuesare set differently between the bright area 92 and the dark are 93,thereby representing the object using the color values of two grades. Inthis manner, the conventional technology generates a cartoon-like imagein gradual shades.

[0006] In some cases, a game apparatus or a game system shades theobject in accordance with a special effect generated in a game space.For example, the object is shaded so as to be viewed as if it isilluminated by lightning or explosion, as well as by a normal light beamprovided in the game space. Also, there may be a case where the objectis shaded so as to be viewed as if it is illuminated by light beams fromtwo or more places without using a light beam provided as a specialeffect, e.g., lightning or explosion.

[0007] In the above-described conventional technology, however, thestate of the object illuminated by the light beams from two or moreplaces cannot be represented using toon shading. This is because thebrightness information used with toon shading in the conventionaltechnology is defined by a prescribed condition (e.g., the virtual light91 as described above), and therefore the brightness information cannotbe used for representing a light beam (e.g., a light beam provided as aspecial effect) different from the normal light beam. Specifically, inthe example of FIG. 12, the brightness information is defined by thelight beam illuminating the object from the position of the virtuallight 91, and therefore even if the brightness information is used, thestate of the object illuminated by a light beam from a position otherthan the position of the virtual light 91 cannot be represented.

[0008] Accordingly, in the conventional technology, the state of theobject illuminated by the light beam provided as a special effect isrepresented by shading the object without using toon shading, or such astate is represented without shading the object. As a result, in theconventional technology, the object to be represented as a cartoon-likeobject is realistically shaded, or the object is not shaded at all.Therefore, the state of the object illuminated by the light beams fromtwo or more places, typically, as in the case where the light beamprovided as a special effect is used, cannot be satisfactorilyrepresented using toon shading, resulting in an unnatural image. Inorder to shade the object so as to be viewed as if it is illuminated bythe light beams from two or more places, an extra process is required inaddition to toon shading, leading to an increase in number of processesfor image generation. Thus, in some cases, the above-describedconventional technology cannot be used in a game apparatus or the likewhich requires real-time image generation.

SUMMARY OF THE INVENTION

[0009] Therefore, an object of the present invention is to provide agame apparatus and game program capable of representing the state of anobject illuminated by light beams from two or more places using the toonshading.

[0010] The present invention has the following features to attain theobject mentioned above. It should be noted that reference numerals andsupplemental remarks in brackets are provided in the followingdescription in order to indicate correspondence with embodiments, whichwill be described for facilitating easy understanding of the presentinvention, rather than to limit the scope of the present invention.

[0011] A first aspect of the present invention is directed to a gameapparatus (a game apparatus 101) for displaying an object in a gamespace. The game apparatus includes: a light source setting section (aCPU 202 and/or a GPU 204 implementing steps S12 and Sl4; hereinafter,only step numbers are shown); a brightness calculating section (abrightness calculating section 521 and a texture coordinate generatingsection 522, S21 and S22); a threshold value storage section (athreshold value data storage region 205 e); a region determining section(a texture color determining section 523, S23 through S29); and adisplay color determining section (a display color determining section524, S30). The light source setting section sets, in the game space, nlight sources (a normal light 64 and an effect light 65) (where n is aninteger equal to or more than 2) for irradiating the object with a lightbeam. The brightness calculating section calculates, for each ofpredetermined units forming the object, a brightness vector having ascomponents n illumination intensities (first and second illuminationintensities) respectively added by the n light sources. The thresholdvalue storage section has threshold values of the n illuminationintensities (first and second threshold values) stored therein. Thethreshold values are used for dividing a coordinate region for thebrightness vector into at least three regions (first through fourregions). The region determining section determines, for each of thepredetermined units, a region including a tip of the brightness vectorcalculated by the brightness calculating section from among the regionsobtained via division by the threshold values based on relationships insize between the n illumination intensities and their correspondingthreshold values. The display color determining section determines adisplay color for each of the predetermined units based on the regiondetermined for each of the predetermined units by the region determiningsection, such that the object's display color distinctly varies.

[0012] As described above, in the first aspect, n types of illuminationintensities added by the n light sources are calculated. Toon shading isperformed using an n-dimensional brightness vector having the n types ofillumination intensities as components, and a coordinate region andthreshold value of the brightness vector, and the display color of eachof the predetermined units forming the object is determined. In thismanner, the brightness added by the n light sources is represented usingthe n-dimensional vector and the coordinate region, whereby it ispossible to separately represent influence of n different light beams oneach of the predetermined units. Moreover, since toon shading isperformed using the n-dimensional vector and the coordinate region, andthen the object's display color is determined, it is possible todetermine, for each of the predetermined units, the display color onwhich the influence of the n different light beams are reflected. Thus,it is possible to represent the state of the object illuminated by thendifferent light beams using toon shading.

[0013] Alternatively, in the first apparatus, the light source settingsection may set a first light source (a first light (the normal light64)) emitting a light beam of a first color (red), and a second lightsource (a second light (the effect light 65)) emitting a light beam of asecond color (green) which is different from the first color. Thebrightness calculating section may calculate, for each of thepredetermined units forming the object, a brightness vector composed ofthe illumination intensities corresponding to values of color componentsof the first and second colors. The region determining section maydetermine the region including the tip of the brightness vector bydetermining a relationship in size between the value of the colorcomponent of the first color and its corresponding first thresholdvalue, and a relationship in size between the value of the colorcomponent of the second color and its corresponding second thresholdvalue.

[0014] Accordingly, each illumination intensity is calculated based on acorresponding one of the values of color components of the first andsecond colors, and therefore when calculating an illumination intensityadded by one of the first and second light sources, it is not necessaryto consider the influence of the other light source. That is, eachillumination intensity is calculated based on a value of a differentcolor component, and therefore can be separately calculated. Thus, it ispossible to simultaneously set the two light sources and calculate theillumination intensities added by the two light sources. Moreover, it ispossible to accurately calculate an illumination intensity added by oneof the two light sources without being influenced by the other lightsource.

[0015] Alternatively, still, in the first aspect, the first color may beeither one of red, green, or blue. In this case, the second colordiffers from the first color, and is either one of red, green, or blue.

[0016] Thus, it is possible to represent the illumination intensitiesusing each component value of color data represented by RGB values.

[0017] Alternatively still, in the first aspect, the coordinate regionmay be divided into different regions by the first threshold value, andmay further be divided into different regions by the second thresholdvalue. In this case, the display color determining section determinesdisplay colors of different brightness in accordance with the regionsobtained by division by the first threshold value, and determinesdisplay colors of different types in accordance with the regionsobtained by division by the second threshold value.

[0018] Accordingly, the brightness of the display color of each ofpredetermined units varies in accordance with the illumination intensityadded by the first light source. Also, the brightness of the displaycolor of each of predetermined units varies in accordance with theillumination intensity added by the second light source. Thus, the firstand second light sources can be used for representing shades due tolight beams of different types.

[0019] Alternatively still, in the first aspect, the display colordetermining section may determine, in accordance with the regionsobtained by division by the second threshold value, either a color usedfor representing an object influenced by a special effect generated inthe game space or a color used for representing an object in the casewhere no special effects are generated.

[0020] Thus, the second light source can be used for representing shadesdue to a light beam provided as the special effect. The special effectas described herein refers to lightning or explosion generated in thegame space.

[0021] Alternatively still, in the first aspect, the game apparatus mayfurther include a special effect determining section (S13). The specialeffect determining section determines whether the special effect isgenerated in the game space. The light source setting section providesthe second light source only when the special effect determining sectiondetermines that the special effect has been generated.

[0022] Accordingly, it is possible to irradiate the object with thelight beam provided as the special effect when necessary, i.e., onlywhen the special effect is generated. Thus, it is possible to representthe state of the object illuminated by the special effect which istemporarily generated.

[0023] Alternatively still, in the first aspect, the game apparatus mayfurther include a display color storage section (a basic display colordata storage region 205 d). The display color storage section has basicdisplay colors stored therein. The basic display colors are used fordetermining the display color of each object. In this case, the displaycolor determining section determines the display color based on theregion determined by the region determining section and the basicdisplay colors stored in the display color storage section.

[0024] Alternatively, still, in the first aspect, the region determiningsection may represent a determined region by a numerical value. Thedisplay color determining section may determine the display color byperforming a predetermined calculation using the numerical valuerepresenting the region determined by the region determining section andcolor data for the basic display colors.

[0025] Accordingly, it is possible to determine the display color byperforming the predetermined calculation, and therefore it is notnecessary to prepare a table in which the region determined by theregion determining section is associated with the basic display colors,for example. Thus, it is possible to conserve a storage region of thegame apparatus.

[0026] A second aspect of the present invention is directed to a gameapparatus for displaying an object in a game space. The apparatusincludes: a first light source setting section (S12); a second lightsource setting section (S14); a brightness calculating section (thebrightness calculating section 521 and the texture coordinate generatingsection 522, S21 and S22); a threshold value storage section (thethreshold value data storage region 205 e); a first detecting section(the texture color determining section 523, S23); a second detectingsection (the texture color determining section 523, S24 and S25); and adisplay color determining section (the display color determining section524, S30). The first light source setting section sets, in the gamespace, a first light source (the normal light 64) for irradiating theobject with a light beam. The second light source setting section sets,in the game space, a second light source (the effect light 65) which isdifferent from the first light source. The brightness calculatingsection calculates, for each of predetermined units forming the object,a first illumination intensity added by the first light source and asecond illumination intensity added by the second light source. Thethreshold value storage section has threshold values of the first andsecond illumination intensities stored therein. The first detectingsection detects, for each of the predetermined units, a relationship insize between the first illumination intensity and its correspondingthreshold value. The second detecting section detects, for each of thepredetermined units, a relationship in size between the secondillumination intensity and its corresponding threshold value. Thedisplay color determining section determines a display color for each ofthe predetermined units based on detection results obtained for each ofthe predetermined units by the first and second detecting sections, suchthat the object's display color distinctly varies.

[0027] As described above, in the second aspect, two types ofillumination intensities added by the two light sources are calculated.Toon shading is performed using the illumination intensities and thethreshold values, and the display color of each of the predeterminedunits forming the object is determined. In this manner, the brightnessadded by the two light sources is represented using the two types ofillumination intensities, whereby it is possible to separately representinfluence of two different light beams on each of the predeterminedunits. Moreover, since toon shading is performed using the twoillumination intensities, and then the object's display color isdetermined, it is possible to determine, for each of the predeterminedunits, the display color on which the influence of the two differentlight beams are reflected. Thus, it is possible to represent the stateof the object illuminated by the two different light beams using toonshading.

[0028] In the first and second aspects, the predetermined units aretypically polygons forming the object.

[0029] A third aspect of the present invention is directed to acomputer-readable recording medium having a game program recordedtherein. The game program causes a game apparatus to implement functionsachieved by the first aspect.

[0030] A fourth aspect of the present invention is directed to acomputer-readable recording medium having a game program recordedtherein. The game program causes a game apparatus to implement functionsachieved by the second aspect.

[0031] These and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is an external view of a game system according to anembodiment of the present invention;

[0033]FIG. 2 is a block diagram illustrating a structure of the gamesystem illustrated in FIG. 1;

[0034]FIG. 3 is a diagram illustrating what data is stored in whichregion of a DVD-ROM 102;

[0035]FIG. 4 is a diagram illustrating what data is stored in whichregion of a main memory 205;

[0036]FIG. 5 is a diagram illustrating functional elements of the gameapparatus illustrated in FIG. 1;

[0037]FIG. 6A is a diagram illustrating a texture coordinate system usedin an embodiment of the present invention;

[0038]FIG. 6B is a diagram illustrating a texture coordinate system usedin another embodiment of the present invention;

[0039]FIG. 7 is a diagram illustrating the relationship among color dataused in the game apparatus illustrated in FIG. 1;

[0040]FIG. 8 is a flowchart illustrating the procedure of gameprocessing performed in accordance with a collaborative operation of aCPU 202 and a GPU 204 of the game apparatus illustrated in FIG. 1;

[0041]FIG. 9 is a flowchart illustrating the details of step S16 shownin FIG. 8;

[0042]FIG. 10 is a diagram illustrating an exemplary display of anobject displayed in the case where a special effect is generated;

[0043]FIG. 11 is a diagram illustrating an exemplary display of anobject displayed in the case where no special effects are generated; and

[0044]FIG. 12 is a diagram illustrating an exemplary display of an imagegenerated by a conventional technology using toon shading.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045]FIG. 1 is an external view of a game system according to anembodiment of the present invention. FIG. 2 is a block diagramillustrating a structure of the game system illustrated in FIG. 1. Asshown in FIGS. 1 and 2, the game system includes: a game apparatus 101;a DVD-ROM 102; an external memory card 103; a controller 104; aloudspeaker 201; and a television receiver 105 (hereinafter, simplyreferred to as the “television 105”). The DVD-ROM 102 and the externalmemory card 103 are removably placed within the game apparatus 101. Thetelevision 105 is connected to the game apparatus 101 via an AV cable106. The controller 104 is connected via a communication cable 107 toany one of a plurality of controller port connectors provided in thegame apparatus 101 (in FIG. 1., four of such connectors are shown). Inother embodiments, communication between the game apparatus 101 and thecontroller 104 may be performed via radio without using thecommunication cable 107. Each element of the game system according tothe present embodiment will be described in detail below with referenceto FIG. 2.

[0046] The DVD-ROM 102, which is described as an exemplary externalrecording medium usable in the present invention, includes permanentlystored data related to a game, e.g., a game program, character data,etc. When the player plays the game, the DVD-ROM 102 is placed withinthe game apparatus 101. Note that a means for storing the game program,etc., is not limited to the DVD-ROM 102, and a recording medium, such asa CD-ROM, an MO, a memory card, a ROM cartridge, or the like, can beused for storing the game program. The external memory card 103 isformed by a rewritable recording medium, such as a flash memory, andtypically stores data, such as save data of the game.

[0047] The game apparatus 101 reads the game program stored in theDVD-ROM 102, and performs game processing. Details of the structure ofthe game apparatus 101 will be described later. The controller 104 is aninput device for the player to input information related to gameoperation, and includes a plurality of operating switches. Thecontroller 104 outputs operation data to the game apparatus 101, forexample, in response to the player pressing an operating switch. Thetelevision 105 displays on its screen image data outputted by the gameapparatus 101. The loudspeaker 201 is typically included in thetelevision 105, and produces sound which is generated during the gameand outputted by the game apparatus 101.

[0048] Next, the structure of the game apparatus 101 is described indetail. Referring to FIG. 2, the game apparatus 101 includes a CPU 202and a memory controller 203 connected thereto. In the game apparatus101, the memory controller 203 is further connected to a graphicsprocessing unit (GPU) 204, a main memory 205, and a plurality ofinterfaces (I/Fs) 208 through 212. The memory controller 203 is alsoconnected to a sub-memory 207 via a digital signal processor (DSP) 206.The memory controller 203 controls data transfer between theabove-mentioned elements.

[0049] In order to start the game, a DVD drive 213 initially drives theDVD-ROM 102 placed within the game apparatus 101. Then, the game programstored in the DVD-ROM 102 is read onto the main memory 205 via a DVDdisc I/F 212 and the memory controller 203. The CPU 202 implements thegame program on the main memory 205, so that the game is started. Afterthe game is started, the player uses the operating switches of thecontroller 104 to provide inputs related to game operation or the like.In accordance with the inputs provided by the player, the controller 104outputs operation data to the game apparatus 101. The operation dataoutputted by the controller 104 is inputted to the CPU 202 via acontroller I/F 208 and the main controller 203. The CPU 202 performsgame processing in accordance with the operation data inputted. The GPU204 and the DSP 206 are used for generating image data during the gameprocessing, for example. The sub-memory 207 is used when the DSP 206performs prescribed processing.

[0050] The GPU 204 includes a geometry unit 214 and a rendering unit215. The geometry unit 214 performs arithmetic processing regardingcoordinates of a three-dimensional model (e.g., an object formed bypolygons) related to an object or graphics placed in a game space, whichis a virtual three-dimensional space. Examples of such arithmeticprocessing include the rotation, scaling, and deformation of thethree-dimensional model, and coordinate conversions from the worldcoordinate system to the viewing coordinate system or screen coordinatesystem. Based on a prescribed texture (which is used for forming adesign or patterns and is different from the texture as used in the term“texture color” which will be described later), the rendering unit 215generates a game image by writing to a color buffer 216 color data (RGBdata) of each pixel of the three-dimensional model projected onto thescreen coordinate system. The GPU 204 uses portion of the main memory205 as memory for image processing (e.g., a frame memory region 205 f asshown in FIG. 4). The GPU 204 uses the geometry unit 214 and therendering unit 215 to generate image data to be displayed on thetelevision 105 and suitably outputs the image data to the television 105via the memory controller 203 and a video I/F 209. Audio data generatedby the CPU 202 during the implementation of the game program isoutputted via the memory controller 203 through an audio I/F 211 to theloudspeaker 201. In the present embodiment, the portion of the mainmemory 205 is used as the memory for image processing. However, hardwareconfiguration including an additional memory exclusively used for imageprocessing can be employed.

[0051]FIG. 3 is a diagram illustrating what data is stored in whichregion of the DVD-ROM 102. The DVD-ROM 102 includes:

[0052] a program region 102 a; an image data region 102 b; an audio dataregion 102 c; and a set of other regions 102 d. In the program region102 a, a main program of the game, a texture process program, and otherprograms are stored. The texture process program is used for causing thegame apparatus to perform a process for setting display colors ofpolygons, which form the object, using toon shading. The details of thisprocess will be described later.

[0053] In the image data region 102 b, for example, object data, whichincludes data related to polygons forming objects and data related totextures of the objects, is stored. In the audio data region 102 c, datafor background music (BGM) of the game, sound effects during the game,etc., is stored.

[0054]FIG. 4 is a diagram illustrating what data is stored in whichregion of the main memory 205. The main memory 205 includes a programdata storage region 205 a; a polygon data storage region 205 b; atexture color data storage region 205 c; a basic display color datastorage region 205 d; a threshold value data storage region 205 e; aframe memory region 205 f; and a set of other regions 205 g. In theprogram data storage region 205 a, the game program (including the mainprogram, the texture process program, etc.), which is read from theDVD-ROM 102 when the game is started, is stored. In the polygon datastorage region 205 b, data for polygons used for forming an object isstored.

[0055] In the texture color data storage region 205 c, color data fortexture colors, which are generated by toon conversion during a textureprocess as described later, is stored. In the present embodiment, thecolor data stored includes data for four texture colors, i.e., black,red, green, and yellow. The texture color data is represented by RGBvalues. As described above, the texture as used in the term “texturecolor” is different from the texture used for forming a design orpatterns on an object.

[0056] In the basic display color data storage region 205 d, color data(RGB values) for basic display colors used for determining the displaycolor of the object is stored. In the present embodiment, three types ofbasic display color data are stored for each object. The three types ofbasic display colors are separately referred to as the “first basicdisplay color”, the “second basic display color”, and the “third basicdisplay color”. Specifically, the first basic display color representsthe object in a normal state (where no special effects are added), andis relatively darker than the second basic display color. The secondbasic display color represents the object in a normal state, and isrelatively lighter than the first basic display color. The third basicdisplay color is also referred to as the “effect display color”, andrepresents the object in the state of being influenced by a specialeffect generated in the game space. The term “special effect” asdescribed herein refers to, for example, lightning or explosiongenerated in the game space. For example, in the case where the objectis a green cap, dark green is set as the first basic display color, andlight green color is set as the second basic display color. Moreover, acolor, e.g., pale blue, which indicates that the cap is illuminated bythe lightning, is set as the third basic display color. Typically, thethird basic display color is set so as to be different in type from thefirst and second basic display colors.

[0057] In the threshold value data storage region 205 e, first andsecond threshold values are stored. These values are used for performingtoon conversion during the texture process as described later. Note thata plurality of first threshold values may be stored, and similarly, aplurality of second threshold values may be stored. Specifically, bysetting the plurality of first and/or second threshold values, it ispossible to divide a coordinate region of a coordinate system, whichwill be described in conjunction with FIG. 6, into at least six regions.Detailed description as to the division of the coordinate region will begiven later.

[0058] The frame memory region 205 f is used as memory for imageprocessing by the GPU 204. In the frame memory region 205 f, forexample, color buffers or z-buffers are assigned. In the set of otherregions 205 g, variables used for the game processing other than thevalues and data described above are stored.

[0059] Next, feature parts of the game apparatus according to thepresent embodiment will be described with reference to FIGS. 5, 6A, and6B. FIG. 5 is a conceptual diagram illustrating the feature parts, i.e.,functional elements, of the game apparatus according to the presentembodiment. The game apparatus performs the toon shading on an object ina three-dimensional game space in order to set distinctly varyingdisplay colors (shades). In the game apparatus, two light sources(lights) are used for toon shading, and the two light sources enablesetting of three types of display colors (a light color, a dark color,and a color used for a special effect) for each object. Accordingly, thegame apparatus is able to represent the state of the object illuminatedby light beams from two or more places with a cartoon-like image (such astate will be described later with reference to FIG. 10). The outline ofthe operation of the game apparatus will be described below.

[0060] In FIG. 5, the game apparatus includes a polygon processingsection 51, a texture processing section 52, and a video signalgenerating section 53. The polygon processing section 51 initially formsan object to be displayed using polygons. In the present embodiment, atexture process is performed on each of the polygons forming the object.Specifically, the texture processing section 52 determines a displaycolor for each polygon. The texture processing section 52 is describedin detail below.

[0061] As illustrated in FIG. 5, the texture processing section 52includes: a brightness calculating section 521; a texture coordinategenerating section 522; a texture color determining section 523; adisplay color determining section 524; and a texture combining section525. The brightness calculating section 521 calculates brightness addedby lights with respect to each vertex of the polygons. The followingdescription is provided with respect to a case (as shown in FIG. 10)where two virtual lights for the toon shading process are provided inthe game space where the object is present. In the present embodiment,the two virtual lights are respectively referred to as the “first light”and the “second light”. The first light is a red light for emitting ared light beam, and the second light is a green light for emitting agreen light beam. The brightness calculating section 521 calculatesbrightness added by each of the two lights. Herein, the brightness addedby a given light is referred to as the “illumination intensity”. Morespecifically, the brightness added by the first light is referred to asthe “first illumination intensity”, and the brightness added by thesecond light is referred to as the “second illumination intensity”. Inthe present embodiment, the brightness calculating section 521calculates the first illumination intensity added by the first light(the red light), and the second illumination intensity added by thesecond light (the green light). A vector having the first and secondillumination intensities as its components is referred to as the“brightness vector”.

[0062] Herein, the first illumination intensity refers to a value of anR component of color data (represented by RGB values) at a vertex of apolygon; and the second illumination intensity refers to a value of a Gcomponent of the color data at the vertex of the polygon. That is, thebrightness calculating section 251 calculates the first illuminationintensity by extracting the R component from the color data (R,G,B) atthe vertex of the polygon, and calculates the second illuminationintensity by extracting the G component from the color data (R,G,B) atthe vertex of the polygon. Accordingly, in the case where the color dataat the vertex of the polygon is represented by, for example, (R₁,G₁,B₁),(R₁,G₁) is obtained as a brightness vector. In the followingdescription, the color data is represented by R, G, and B componentseach represented in 256 shades of color. In other embodiments, anymethod, including a method which uses color data for a polygon coloredby virtual lights, may be used for calculating each component (eachillumination intensity) of the brightness vector.

[0063] The texture coordinate generating section 522 generates a texturecoordinate value (S,T) based on the first and second illuminationintensities. The texture coordinate value is a two-dimensional vectorrepresenting illumination intensities added by the above-described twolights. That is, the texture coordinate value is the brightness vector.Note that the value of the first illumination intensity is used as the Scomponent of the texture coordinate value, and the value of the secondillumination intensity is used as the T component of the texturecoordinate value. That is, in the present embodiment, the value of the Rcomponent of the color data at the vertex of the polygon corresponds tothe value of the S component, and the value of the G component of thecolor data at the vertex of the polygon corresponds to the value of theT component. The texture color determining section 523 determines atexture color based on the texture coordinate value generated in theabove-described manner. A texture coordinate system and the texturecolor are described below with reference to FIGS. 6A and 6B.

[0064]FIG. 6A is a diagram illustrating the texture coordinate systemused in the present embodiment. In the texture coordinate systemillustrated in FIG. 6A, the horizontal axis represents a value of the Scomponent, and the vertical axis represents a value of the T component.That is, the texture coordinate system is a coordinate region defined bythe coordinate axes each representing a component of the brightnessvector. A first threshold value is set for the horizontal axis (the Scomponent), and a second threshold value is set for the vertical axis(the T component). In FIG. 6A, both the first and second thresholdvalues are 127. The coordinate region of the texture coordinate systemis divided into four regions (first through fourth regions) withreference to the first and second threshold values. Four texture colors,i.e., black, red, green, and yellow, are assigned to the four regions.The texture color determining section 523 determines a texture colorusing the texture coordinate system as described above. Specifically,the display color of the object is determined in accordance with thecoordinate regions obtained via the division by the threshold values.That is, the display colors are determined based on which one of theregions obtained via the division by the threshold values includes atexture coordinate value (the tip of the brightness vector).

[0065] In the present embodiment, when the texture coordinate value isincluded in the first region (when the texture color is black), a darkcolor (a first basic display color) representing dark portion of theobject is set as the display color. Alternatively, when the texturecoordinate value is included in the second region (when the texturecolor is red), a light color (a second basic display color) representinga bright portion of the object is set as the display color. Thus, it isappreciated that display colors having different brightness are set inaccordance with the relationship in size between the first illuminationintensity and the first threshold value. When the texture coordinatevalue is included in the third or fourth region (when the texture coloris green or yellow), an effect display color (a third basic displaycolor) is set as the display color. Thus, it is appreciated that thedisplay color is set by selecting either the color of the object towhich a special effect is added or the color of the object in a normalstate in accordance with the relationship in size between the secondillumination intensity and the second threshold value. In the presentembodiment, eventually, the same color is set as the display color whenthe texture coordinate value is included in either the third or fourthregion, and therefore the third and fourth regions may be considered asone region.

[0066] In order to clarify the feature of the present invention, a caseof determining the texture color when only one light is used isdescribed with reference to FIG. 6B. When only one light is used (inthis case, the red light is used), only one illumination intensity isdetected at a polygon, and therefore the two-dimensional texturecoordinate system as illustrated in FIG. 6A is not used. In FIG. 6B,either one of two texture colors (black or red) is selected inaccordance with the relationship in size between a threshold value andthe illumination intensity detected at the polygon.

[0067] The following is a detailed description as to how the texturecolor is determined in accordance with the present embodiment. Thetexture color determining section 523 detects the relationship in sizebetween the value of the S component and the first threshold value.Specifically, it is determined whether the value of the S component isgreater than the first threshold value. In other words, the value of theS component represented in 256 shades of color is converted into a valuerepresented in two shades of color in accordance with the size relativeto the first threshold value. Similar to the S component, the value ofthe T component represented in 256 shades of color is converted into avalue represented in two shades of color in accordance with the sizerelative to the second threshold value. In this manner, toon conversionis performed. Which one of the four regions of the texture coordinatesystem includes the texture coordinate value (the brightness vector)(S,T) can be known from the relationship in size between the value ofthe S component and the first threshold value and the relationship insize between the value of the T component and the second thresholdvalue. Since the four regions have their respective texture colorsassigned thereto, the texture color can be determined based on whichregion includes the texture coordinate value. For example, in the caseof the texture coordinate value (10,10), the coordinate value is presentin the first region, and therefore the texture color is determined asblack. Alternatively, in the case of the texture coordinate value(230,10), the coordinate value is present in the second region, andtherefore the texture color is determined as red. In this manner, thetexture color of the polygon is obtained based on the illuminationintensities of the two lights.

[0068] The display color determining section 524 determines the displaycolor of each polygon in accordance with the region including thetexture coordinate value, i.e., in accordance with the texture color.Specifically, display colors of polygons are determined based on texturecolors assigned to four regions. Accordingly, one of four or less colors(in the present embodiment, three colors) is selected as the displaycolor of each polygon, and therefore the object is displayed such thatthe display color thereof distinctly varies, i.e., a cartoon-like objectis displayed. Note that display color data indicating the display coloris represented by RGB values. Specifically, in the present embodiment,the display color is determined based on the texture color and a basicdisplay color predetermined for the object. Detailed description as tohow the display color is determined in accordance with the presentembodiment will be provided later.

[0069] The texture combining section 525 converts the display colordetermined by the display color determining section 524 into a shadingcolor, and generates video color data by combining the shading colorwith image data representing a texture, i.e., a design or patterns,which is predetermined for each polygon of the object. The video colordata as described herein refers to data representing a video color fordetermining a display state as to how the object is displayed on thetelevision 105. Note that the above-described texture (a design orpatterns) is different from the texture described in conjunction withthe texture coordinate generating section 522 and the texture colordetermining section 523. In the case where it is not necessary to form adifferent design or different patterns for each polygon, the displaycolor maybe used as the video color.

[0070] The video signal generating section 53 generates a display signalfor displaying an image on the television 105, based on the video colordata generated by the texture processing section 52. The video signalgenerating section 53 corresponds to the video I/F 209 illustrated inFIG. 2. As described above, the game apparatus according to the presentembodiment obtains a value of a multi-dimensional illumination intensity(a brightness vector) using two or more lights, thereby making itpossible to use toon shading to display the state of the objectilluminated by light beams from two or more places.

[0071] Next, detailed description as to how the display color isdetermined in accordance with the present embodiment is described withreference to FIG. 7. FIG. 7 is a diagram illustrating the relationshipamong color data used in the game apparatus according to the presentembodiment. As described above, texture colors (black, red, green, andyellow) of polygons forming the object are initially determined by twolights having different colors (red and green lights). In the presentembodiment, a mixture ratio (α) and an addition ratio (β) are obtainedfor each texture color determined in a manner as described above. Eachtexture color has its values of the mixture ratio and addition ratio,and for example, the game apparatus previously stores a table in whicheach texture color is associated with a pair of a mixture ratio and anadditional ratio. Further, different values of the mixture ratio andaddition ratio are provided for each texture color. For example, an Rcomponent of color data for a texture color may be used as the value ofthe mixture ratio, and a G component of the color data for the texturecolor may be used as the value of the addition ratio.

[0072] The display color is determined based on the mixture and additionratios previously determined in a manner as described above, and basedon the basic display color stored in the main memory 205. Specifically,the display color is determined based on the following expression (1)using the mixture and addition ratios and the basic display color,

(Display color)=(C ₁)×α+(C ₂)×(1−α)+(C ₃)×β  (1),

[0073] where C1 is color data for a first basic display color, C2 iscolor data for a second basic color, C3 is color data for a third basicdisplay color, a is a mixture ratio, and P is an additional ratio. Here,the mixture ratio α is a value within the range from 0 to 1 which isdetermined based on the value (0 to 255) of the R component of thetexture color; the addition ratio β is a value within the range from 0to 1 which is determined based on the value (0 to 255) of the Gcomponent of the texture color. As described above, the display color isgenerated so as to be represented by RGB values, and therefore theexpression (1) can be represented by:

O _(r)=(C _(1r))×α+(C _(2r))×(1−α)+(C _(3r))×β  (2);

O _(g)=(C _(1g))×α+(C _(2g))×(1−α)+(C _(3g))×β  (3); and

O _(b)=(C _(1b))×α+(C _(2b))×(1−α)+(C _(3b))×β  (4),

[0074] where O_(r) is the R component of the display color, O_(g) is theG component of the display color, and O_(b) is the B component of thedisplay color. C_(1r), C_(1g), and C_(1b) are the R component, the Gcomponent, and the B component, respectively, of C₁. Similar to C_(1r),C_(1g), and C_(1b), C_(2r), C_(2g), and C_(2b) are the R component, theG component, and the B component, respectively, of C₂, and C_(3r),C_(3g), and C_(3b) are the R component, the G component, and the Bcomponent, respectively, of C₃. In the display color determining section524, the above expressions (2) through (4) are used to calculate the RGBvalues of the display color data. Note that in the case of using themixture and addition ratios, a final display color may or may not be thesame as any one of the first through third basic display colorsdepending on how the mixture and addition ratios are set. Even in such acase, the final display color consists of three (or four) colorcomponents.

[0075] As described above, in the present embodiment, the mixture andaddition ratios are determined in accordance with the texture color, andthe display color is determined in accordance with the mixture andaddition ratios. In other embodiments, the basic display color may bedirectly determined as the display color in accordance with the texturecolor. Specifically, a table in which texture colors are associated withbasic display colors is previously prepared for each object, and a basicdisplay color, which is uniquely determined in accordance with a texturecolor of a target polygon, is determined as the display color of thatpolygon. For example, when the texture color is black, the first basicdisplay color is determined as the display color. Alternatively, whenthe texture color is red, the second basic display color is determinedas the display color. Alternatively still, when the texture color isgreen or yellow, the third basic display color is determined as thedisplay color. On the other hand, the present embodiment uses themixture and addition ratios, and therefore it is not necessary toprepare such a table as described above, so that memory of the gameapparatus can be saved.

[0076] Next, processing performed by the game apparatus according to thepresent embodiment is described in detail. FIG. 8 is a flowchartillustrating the procedure of game processing performed in accordancewith a collaborative operation of the CPU 202 and the GPU 204 of thegame apparatus. In the present embodiment, although the game processingis performed in accordance with a collaborative operation of the CPU 202and the GPU 204, it is possible to enable, for example, only the CPU 202to perform substantially the entire game processing including geometryprocessing.

[0077] Upon the start of the game, initial setting is performed at stepS11. Specifically, the initial setting includes initialization ofvariables used in the game processing, formation of the game space, etc.Next, at step S12, a first light is set in a predetermined position ofthe game space. Here, it is assumed that the first light emits a redlight beam as described above. The first light is used for adding anormal shading effect (a shading effect in the case where no specialeffect is generated) to the object. Accordingly, in the followingdescription, the first light is interchangeably referred to as the“normal light”. The term “special effect” as described herein refers toan event generated during the game, such as lightning or explosion,which necessitates a virtual light to irradiate the object with a lightbeam. The special effect may be generated when a predetermined conditionis satisfied during the game, e.g., when a bomb is exploded.Alternatively, the special effect may be generated by the player'soperation.

[0078] Following step S12, at step S13, it is determined whether thespecial effect is generated in the game space. At step S13, if it isdetermined that the special effect is generated, processes at step S14and S15 are sequentially performed. On the other hand, if it is notdetermined that the special effect is generated, step S14 is skipped andthe process at step S15 is performed immediately after step S13.

[0079] At step S14, a second light is set in a predetermined position inthe game space. Here, it is assumed that the second light emits a greenlight beam as described above. The second light is used for shading theobject as a result of a special effect. Accordingly, in the followingdescription, the second light is interchangeably referred to as the“effect light”.

[0080] At step S15, a polygon process is performed on the object.Specifically, polygons are generated to form the object in the gamespace. Note that the process at step S15 corresponds to an operationperformed by the polygon processing section 51 illustrated in FIG. 5. Atthe subsequent step S16, a texture process is performed. The textureprocess corresponds to an operation performed by the texture processingsection 52 illustrated in FIG. 5. The details of the texture process aredescribed below.

[0081]FIG. 9 is a flowchart illustrating the details of step S16 shownin FIG. 8. First, at step S21, an illumination intensity is calculatedfor each vertex of the polygons generated at step S15. Specifically, avalue of the R component of color data of each vertex of the polygons iscalculated as a first illumination intensity, and a value of the Gcomponent of color data of each vertex of the polygons is calculated asa second illumination intensity. The process at step S21 corresponds toan operation performed by the brightness calculating section 521illustrated in FIG. 5.

[0082] At step S22, texture coordinates (S,T) are generated based on thefirst and second illumination intensities calculated at step S21.Specifically, a value of the first illumination intensity is obtained asthe value of the S component of the texture coordinates, and a value ofthe second illumination intensity is obtained as the value of the Tcomponent of the texture coordinates. The process at step S22corresponds to an operation performed by the texture coordinategenerating section 522 illustrated in FIG. 5. A brightness vector iscalculated by performing the above-described steps S21 and S22.

[0083] Following step S22, texture colors are determined at steps S23through S29. That is, processes at steps S23 through S29 corresponds toan operation performed by the texture color determining section 523illustrated in FIG. 5. First, at step S23, it is determined whether thevalue of the S component of the texture coordinates is greater than afirst threshold value. Specifically, by comparing the value of the Scomponent of the texture coordinates generated at step S22 (i.e., thefirst illumination intensity) with the first threshold value stored inthe threshold data storage region 205 e, the relationship in sizebetween these values is determined. If it is determined at step S23 thatthe value of the S component of the texture coordinates is smaller thanthe first threshold value, the process at step S24 is performed. On theother hand, if it is determined at step S23 that the value of the Scomponent of the texture coordinates is greater than the first thresholdvalue, the process at step S25 is performed.

[0084] At step S24, it is determined whether the value of the Tcomponent of the texture coordinates is smaller than a second thresholdvalue. Specifically, by comparing the value of the T component of thetexture coordinates generated at step S22 (i.e., the second illuminationintensity) with the second threshold value stored in the threshold datastorage region 205 e, the relationship in size between these values isdetermined. If it is determined at step S24 that the value of the Tcomponent of the texture coordinates is smaller than the secondthreshold value, the process at step S26 is performed. On the otherhand, if it is determined at step S24 that the value of the T componentof the texture coordinates is greater than the second threshold value,the process at step S27 is performed.

[0085] At step S25, a process similar to that performed at step S24 isperformed. Specifically, if it is determined at step S25 that the valueof the T component of the texture coordinates is smaller than the secondthreshold value, the process at step S28 is performed. On the otherhand, if it is determined at step S25 that the value of the T componentof the texture coordinates is greater than the second threshold value,the process at step S29 is performed.

[0086] At step S26, the texture color is determined as black.Specifically, color data (0,0,0) for black stored in the texture colordata storage region 205 c is selected as texture color data. In thismanner, the texture color is determined as black in the case where acolor at a vertex of a polygon colored by the first and second lights isclose to black, i.e., in the case where the first illumination intensityis smaller than the first threshold value and the second illuminationintensity is smaller than the second threshold value.

[0087] Alternatively, at step S27, the texture color is determined asgreen. Specifically, color data (0,255,0) for green stored in thetexture color data storage region 205 c is selected as the texture colordata. In this manner, the texture color is determined as green in thecase where a color at a vertex of the polygon colored by the first andsecond lights is close to green, i.e., in the case where the firstillumination intensity is smaller than the first threshold value and thesecond illumination intensity is greater than the second thresholdvalue.

[0088] Alternatively still, at step S28, the texture color is determinedas red. Specifically, color data (255,0,0) for red stored in the texturecolor data storage region 205 c is selected as the texture color data.In this manner, the texture color is determined as red in the case wherea color at a vertex of the polygon colored by the first and secondlights is close to red, i.e., in the case where the first illuminationintensity is greater than the first threshold value and the secondillumination intensity is smaller than the second threshold value.

[0089] Alternatively still, at step S29, the texture color is determinedas yellow. Specifically, color data (255,255,0) for yellow stored in thetexture color data storage region 205 c is selected as the texture colordata. In this manner, the texture color is determined as yellow in thecase where a color at a vertex of the polygon colored by the first andsecond lights is close to yellow, i.e., in the case where the firstillumination intensity is greater than the first threshold value and thesecond illumination intensity is greater than the second thresholdvalue.

[0090] Following the process at either one of steps S26 through S29, atstep S30, the display color of the polygon is determined based on thetexture color data. Specifically, the mixture and addition ratios areinitially determined based on the texture color data. Next, the RGBvalues of the display color are determined by substituting into theabove expressions (2) through (4) the mixture and addition ratios andthe color data for the first through third basic display colors storedin the basic display color data storage region 205 d. Note that theprocess at step S30 corresponds to an operation performed by the displaycolor determining section 524 illustrated in FIG. 5.

[0091] Following step S30, a texture combining process is performed atstep S31. Specifically, video color data is generated by combining thedisplay color (the shading color) determined at step S30 with image datarepresenting a texture, i.e., a design or patterns, which ispredetermined for each polygon of the object. Note that the process atstep S31 corresponds to an operation performed by the texture combiningsection 525 illustrated in FIG. 5. After the completion of step S31, thetexture process is completed. The above described texture process isperformed for each polygon of objects in the game space.

[0092] Referring to FIG. 8, at step S17, an image display process isperformed. Specifically, an image is displayed on the television 105based on the video color data generated by the texture process at stepS16. At the subsequent step S18, whether to complete the game isdetermined. For example, it is determined whether the game is over orwhether the player performs an operation for completing the game. If itis determined that the game should not be completed, the procedurereturns to step S12, and a series of processes at steps S12 through S18are repeatedly performed until the game is completed. On the other hand,if it is determined that the game should be completed, the gameprocessing illustrated in FIG. 8 is terminated.

[0093] Described next is an exemplary display of the object displayed bythe game apparatus according to the present embodiment. FIG. 10 is adiagram illustrating an exemplary display of the object displayed in thecase where a special effect is generated. In the case where the specialeffect is generated, a normal light (a red light) 64 and an effect light(a green light) 65 are set (refer to steps S12 through S14 of FIG. 8).By using the two lights as shown in FIG. 10, the toon shading effect canbe enabled even in the case where the object is irradiated with lightfrom different angles. As described above, in the present embodiment,the display color of a single object is selected from three types ofdisplay colors. Specifically, any one of the three types of displaycolors is set for each polygon of the object based on the relationshipin size between the first illumination intensity and the first thresholdvalue, and based on the relationship in size between the secondillumination intensity and the second threshold value. As a result, thesingle object (e.g., the left arm of the gorilla illustrated in FIG. 10)is separated into three parts, i.e., a part 61 for which a brightdisplay color is set, a part 62 for which a dark display color is set,and a part 63 for which a display color provided due to a special effect(the effect display color) is set. In the part 63 for which the effectdisplay color is set, the second illumination intensity is equal to orgreater than the second threshold value (refer to step S27 or S29 inFIG. 9). In the part 61 for which the bright display color is set, thefirst illumination intensity is equal to or greater than the firstthreshold value and the second illumination intensity is smaller thanthe second threshold value. In the part 62 for which the dark displaycolor is set, the first illumination intensity is smaller than the firstthreshold value and the second illumination intensity is smaller thanthe second threshold value.

[0094]FIG. 11 is a diagram illustrating an exemplary display of theobject displayed in the case where no special effects are generated. Inthe case where no special effect are generated, the normal light 64 isset, while the effect light 65 is not set (i.e., turned off). As aresult, the second illumination intensity added to each polygon theobject becomes “0” (S21 of FIG. 9), and the T component of the texturecomponents also becomes “0” (S22 of FIG. 9). Accordingly, the texturecolor is set so as to be black or red (S24 through S29 of FIG. 9), andtherefore the effect color is not set as the display color. Thus, theobject (e.g., the left arm of the gorilla illustrated in FIG. 11) in thecase where no special effects are generated is formed by only the part61 for which the bright display color is set and the part 62 for whichthe dark display color is set.

[0095] Although the above embodiment has been described with respect tothe case where the two lights are set in the game space, three or morelight sources may be used. For example, in the case where three lightsare used, the brightness vector becomes a three-dimensional vector, andthe coordinate region of the texture coordinate system becomes athree-dimensional space. Even in such a case, the display color of eachpolygon can be determined in accordance with regions obtained viadivision by threshold values as can be determined in the above-describedembodiment. Further, since the three lights are present, it is possibleto represent the object illuminated by light beams from three places.Note that in the case of using three lights, it is preferable that red,green, and blue are used as the colors of the lights.

[0096] In the case described in conjunction with FIG. 8, when no specialeffects are generated, no effect light is set (refer to steps S13 andS14 of FIG. 8). In other embodiments, when no special effects aregenerated, neither green nor yellow may be determined as the texturecolor. For example, in the case where no special effects are generated,T=0 may be set at step S22 of FIG. 9, instead of performing the processat step S14 of FIG. 8. This achieves an effect similar to that achievedby the above-described embodiment. Alternatively, in the case where nospecial effects are generated, by making a setting such that thedetermination at each of steps S24 and S25 of FIG. 9 is always positive,it is made possible to achieve an effect similar to that achieved by theabove-described embodiment.

[0097] While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A game apparatus for displaying an object in agame space, the apparatus comprising: a light source setting section forsetting, in the game space, n light sources (where n is an integer equalto or more than 2) for irradiating the object with a light beam; abrightness calculating section for calculating, for each ofpredetermined units forming the object, a brightness vector having ascomponents n illumination intensities respectively added by the n lightsources; a threshold value storage section having threshold values ofthe n illumination intensities stored therein, the threshold valuesbeing used for dividing a coordinate region for the brightness vectorinto at least three regions; a region determining section fordetermining, for each of the predetermined units, a region including atip of the brightness vector calculated by the brightness calculatingsection from among the regions obtained via division by the thresholdvalues based on relationships in size between the n illuminationintensities and their corresponding threshold values; and a displaycolor determining section for determining a display color for each ofthe predetermined units based on the region determined for each of thepredetermined units by the region determining section, such that theobject's display color distinctly varies.
 2. The game apparatusaccording to claim 1, wherein: the light source setting section sets afirst light source emitting a light beam of a first color, and a secondlight source emitting a light beam of a second color which is differentfrom the first color; the brightness calculating section calculates, foreach of the predetermined units forming the object, a brightness vectorcomposed of the illumination intensities corresponding to values ofcolor components of the first and second colors; and the regiondetermining section determines the region including the tip of thebrightness vector by determining a relationship in size between thevalue of the color component of the first color and its correspondingfirst threshold value, and a relationship in size between the value ofthe color component of the second color and its corresponding secondthreshold value.
 3. The game apparatus according to claim 2, wherein:the first color is either one of red, green, or blue; and the secondcolor differs from the first color, and is either one of red, green, orblue.
 4. The game apparatus according to claim 2, wherein: thecoordinate region is divided into different regions by the firstthreshold value, and is further divided into different regions by thesecond threshold value; and the display color determining sectiondetermines display colors of different brightness in accordance with theregions obtained by division by the first threshold value, anddetermines display colors of different types in accordance with theregions obtained by division by the second threshold value.
 5. The gameapparatus according to claim 4, wherein the display color determiningsection determines, in accordance with the regions obtained by divisionby the second threshold value, either a color used for representing anobject influenced by a special effect generated in the game space or acolor used for representing an object in the case where no specialeffects are generated.
 6. The game apparatus according to claim 5,further comprising a special effect determining section for determiningwhether the special effect is generated in the game space, wherein thelight source setting section provides the second light source only whenthe special effect determining section determines that the specialeffect has been generated.
 7. The game apparatus according to claim 1,further comprising a display color storage section having basic displaycolors stored therein, the basic display colors being used fordetermining the display color of each object, wherein the display colordetermining section determines the display color based on the regiondetermined by the region determining section and the basic displaycolors stored in the display color storage section.
 8. The gameapparatus according to claim 7, wherein: the region determining sectionrepresents a determined region by a numerical value; and the displaycolor determining section determines the display color by performing apredetermined calculation using the numerical value representing theregion determined by the region determining section and color data forthe basic display colors.
 9. The game apparatus according to claim 1,wherein the predetermined units are polygons forming the object.
 10. Agame apparatus for displaying an object in a game space, the apparatuscomprising: a first light source setting section for setting, in thegame space, a first light source for irradiating the object with a lightbeam; a second light source setting section for setting, in the gamespace, a second light source which is different from the first lightsource; a brightness calculating section for calculating, for each ofpredetermined units forming the object, a first illumination intensityadded by the first light source and a second illumination intensityadded by the second light source; a threshold value storage sectionhaving threshold values of the first and second illumination intensitiesstored therein; a first detecting section for detecting, for each of thepredetermined units, a relationship in size between the firstillumination intensity and its corresponding threshold value; a seconddetecting section for detecting, for each of the predetermined units, arelationship in size between the second illumination intensity and itscorresponding threshold value; and a display color determining sectionfor determining a display color for each of the predetermined unitsbased on detection results obtained for each of the predetermined unitsby the first and second detecting sections, such that the object'sdisplay color distinctly varies.
 11. The game apparatus according toclaim 10, wherein the predetermined units are polygons forming theobject.
 12. A computer-readable recording medium having a game programrecorded therein, the game program causing a game apparatus to implementa game in which an object is displayed in a game space, the game programcausing the game apparatus to implement: a light source setting step forsetting, in the game space, n light sources (where n is an integer equalto or more than 2) for irradiating the object with a light beam; abrightness calculating step for calculating, for each of predeterminedunits forming the object, a brightness vector having as components nillumination intensities respectively added by the n light sources; aregion determining step for determining, for each of the predeterminedunits, a region including a tip of the brightness vector calculated atthe brightness calculating step from among at least three regions intowhich a coordinate region for the brightness vector is divided bythreshold values of the n illumination intensities, based onrelationships in size between the n illumination intensities and theircorresponding threshold values; and a display color determining step fordetermining a display color for each of the predetermined units based onthe region determined for each of the predetermined units at the regiondetermining step, such that the object's display color distinctlyvaries.
 13. The computer-readable recording medium according to claim12, wherein: the light source setting step sets a first light sourceemitting a light beam of a first color, and a second light sourceemitting a light beam of a second color which is different from thefirst color; the brightness calculating step calculates, for each of thepredetermined units forming the object, a brightness vector composed ofthe illumination intensities corresponding to values of color componentsof the first and second colors; and the region determining stepdetermines the region including the tip of the brightness vector bydetermining a relationship in size between the value of the colorcomponent of the first color and its corresponding first thresholdvalue, and a relationship in size between the value of the colorcomponent of the second color and its corresponding second thresholdvalue.
 14. The computer-readable recording medium according to claim 13,wherein: the first color is either one of red, green, or blue; and thesecond color differs from the first color, and is either one of red,green, or blue.
 15. The computer-readable recording medium according toclaim 13, wherein: the coordinate region is divided into differentregions by the first threshold value, and is further divided intodifferent regions by the second threshold value; and the display colordetermining step determines display colors of different brightness inaccordance with the regions obtained by division by the first thresholdvalue, and determines display colors of different types in accordancewith the regions obtained by division by the second threshold value. 16.The computer-readable recording medium according to claim 15, whereinthe display color determining step determines, in accordance with theregions obtained by division by the second threshold value, either acolor used for representing an object influenced by a special effectgenerated in the game space or a color used for representing an objectin the case where no special effects are generated.
 17. Thecomputer-readable recording medium according to claim 16, wherein: thegame program further causes the game apparatus to implement a specialeffect determining step for determining whether the special effect isgenerated in the game space; and the light source setting step providesthe second light source only when the special effect determining stepdetermines that the special effect has been generated.
 18. Thecomputer-readable recording medium according to claim 12, wherein: thegame apparatus has basic display colors stored therein, the basicdisplay colors being used for determining the display color of eachobject; and the display color determining step determines the displaycolor based on the region determined at the region determining step andthe basic display colors stored in the game apparatus.
 19. Thecomputer-readable recording medium according to claim 18, wherein: theregion determining step represents a determined region by a numericalvalue; and the display color determining step determines the displaycolor by performing a predetermined calculation using the numericalvalue representing the region determined at the region determining stepand color data for the basic display colors.
 20. The computer-readablerecording medium according to claim 12, wherein the predetermined unitsare polygons forming the object.
 21. A computer-readable recordingmedium having a game program recorded therein, the game program causinga game apparatus to implement a game in which an object is displayed ina game space, the game program causing the game apparatus to implement:a first light source setting step for setting, in the game space, afirst light source for irradiating the object with a light beam; asecond light source setting step for setting, in the game space, asecond light source which is different from the first light source; abrightness calculating step for calculating, for each of predeterminedunits forming the object, a first illumination intensity added by thefirst light source and a second illumination intensity added by thesecond light source; a first detecting step for detecting, for each ofthe predetermined units, a relationship in size between the firstillumination intensity and its corresponding threshold value; a seconddetecting step for detecting, for each of the predetermined units, arelationship in size between the second illumination intensity and itscorresponding threshold value; and a display color determining step fordetermining a display color for each of the predetermined units based ondetection results obtained for each of the predetermined units by thefirst and second detecting steps, such that the object's display colordistinctly varies.
 22. The computer-readable recording medium accordingto claim 21, wherein the predetermined units are polygons forming theobject.